After setting up Nagios server and Client you might find to see some funny status messages. One of which is, “Host not reachable” and you will see all the Nagios clients showing up in RED status though other services are fine in status page.
This can happen due to multiple reasons. First one is obviously related to firewall issue. The other one is bit tricky but related to ping
binary which is used by Nagios to ping the ip for check-host-alive
status.
Nagios executes the system binaries using nagios user configured during the installation. Hence, such user must have enough privileges to execute the binary. In the above scenario, ping
must be executable by the user nagios.
To resolve the issue, I added an execute bit on ping binary as follows:
chmod u+s /bin/ping
Restart or wait for Nagios to check the status of the hosts once again. Now I can see that Nagios shows the correct status of the hosts.